The arguments in favor of Einstein are mainly that others credited him (with Germans slighting non-Germans), and that Einstein was responsible for some crucial step or insight that others were missing. This insight is never something Einstein actually said, but rather something that supposedly can be inferred from Einstein's famous paper. Or sometimes the credit is for obscure terminological issues.

Einstein was not particularly influential either, as the chain of development went from Lorentz to Poincare to Minkowski to a wide audience, with hardly anyone paying any attention to Einstein.

My biggest problem with crediting Einstein for SR is something else, tho. It is that he never had a modern geometric understanding of the subject.

The Michelson-Morley experiment could be interpreted as evidence for (1) a stationary Earth; (2) an emitter (non-wave) theory of light; (3) an aether drift theory; or (4) the relativity principle combined with a constant speed of light. FitzGerald and Lorentz reject the first 3 possibilities based on other experiments, and were led to option (4). They then deduced the LT as a logical consequence of those principles. ...

Einstein preferred the principle theory formulation that he got from Lorentz. The Einstein idolizers rave about how great this was, but geometric theory has been the dominant one among theoretical physicists since 1908.

I would call these interpretations top-down, bottom-up, and geometric.

I would suggest that almost the only hypothesis that can reconcile this opposition is that the length of material bodies changes, according as they are moving through the ether or across it, by an amount depending on the square of the ratio of their velocity to that of light.

FitzGerald (and Lorentz) do use the archaic term "ether" (or aether), but Einstein similarly uses the term "stationary" dozens of times in his famous paper with similar epistemological problems.

FitzGerald wrote to Lorentz in 1994:

My dear sir,
I have been for years preaching and lecturing on the doctrine that Michelson's experiment proves, and is one of the only ways of proving, that the length of a body depends on how it is moving through the ether. ...

I am particularly delighted to hear that you agree with me, for I have been rather laughed at for my view over here. I could not ever persuade my own pupil Mr. Preston to introduce this criticism into his book on Light ... [as quoted in paper by Stephen G. Brush]

Einstein used a similar top-down argument in his famous 1905 paper, without mentioning Michelson-Morley, FitzGerald, or Lorentz explicitly. He later said that he was not rejecting the constructive (bottom-up) approach, but could not get it to work.

While Einstein was writing that 1905 relativity paper, Poincare was submitting a paper that had everything Einstein had, and plus the geometric version of the theory. Poincare had the 4D spacetime, the non-Euclidean metric, the symmetry group, the electrodynamic covariance, and the broad vision of spacetime physics that was so important in the XX century.

While most physicists did not read or understand Poincare's paper, Minkowski read it, and spelled out the geometric version of SR in widely accessible terms. Then everyone got excited, and research papers on SR exploded. Some physicists may have thought that Einstein had something to do with progress in relativity, because Einstein and Minkowski refused to credit Poincare, and because Minkowski and Poincare soon died.

One reason the geometric version of SR was so exciting was that it solved the problem of how causality can be reconciled with mechanics. Physicists since Newton had been haunted by what appears to be action-to-distance. The Poincare-Minkowski geometric SR showed that non-Euclidean geometry is the key to understanding that causality takes place withing the light cone.

Poincare showed in 1905 that SR allows gravity theories where gravity propagates at the speed of light. This had been an unsolved problem for centuries. Poincare creates the non-Euclidean geometric view specifically for this purpose. Minkowski elaborated on this much more clearly, and this idea is the basis of all XX century notions of causality.

Einstein missed all of this. He wrote relativity review papers saying "union of Lorentz's theory and the relativity principle" in 1908 and "the essence of Lorentz's theory ... can be reconciled with the relativity principle" in 1909. That is, he affirmed his agreement with how Lorentz reconciled electromagnetism with the relativity principle. He made no mention of the causality or non-Euclidean geometry or covariance that Poincare and Minkowski had spelled out a couple of years earlier. While he always jealously tried to make sure that he got credit for his work, he made no attempt to argue that Poincare and Minkowski were using his ideas, or that he had independently discovered those ideas, or even that he understood or appreciated them. It is preposterous that he is often credited with those ideas today, because he had nothing to do with them.